The Global Positioning System (GPS), the Global Navigation Satellite System (GLONASS), and the satellite navigation system GALILEO are three examples of Global Navigation Satellite Systems (GNSS). A GNSS utilizes an earth-orbiting constellation of a plurality of satellites each broadcasting signals that indicate its precise location and ranging information. From any location on or near the earth, GNSS receivers may normally determine their navigation information by acquiring the satellite signals broadcast from the plurality of GNSS satellites. The time to first fix (i.e. position computation) is enhanced when a GNSS receiver has prior access to a model of satellite orbits and clocks. This model is broadcast by GNSS satellites and is often referred to as ephemeris or ephemeris data. The ephemeris is broadcast to GNSS receivers as part of GNSS broadcasting signals or navigation messages. The broadcast ephemeris comprises navigational information of transmitting GNSS satellites. The navigational information may comprise standard satellite orbit models, clock model, and/or information about the operation status of the related GNSS satellites (healthy or unhealthy), which may be utilized for determining navigational information such as, for example, a position fix and a velocity of a GNSS receiver. The broadcast ephemeris is typically valid for a limited period of time such as 2 to 4 hours into the future (from the time of broadcast). Before the end of the period of validity, the GNSS receiver needs to obtain a fresh broadcast ephemeris to continue operating to produce an accurate position fix and/or velocity of the GNSS receiver.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.